The present invention relates generally to a pressure transducer used with an internal combustion engine in an automobile, and more particularly, to a mini oil pressure transducer used to measure oil pressure and to produce a corresponding indicator signal.
Modern automobiles typically utilize a fuel injection system for the engine which includes an electric motor to power a fuel pump. In addition to providing an oil pressure indicating function, it is sometimes desirable to incorporate an electrical switch mechanism in an oil pressure transducer to control energization of the fuel pump in response to oil pressure. Specifically, it is desirable to activate the fuel pump motor only after a minimum oil pressure is reached.
A number of United States patents generally disclose a pressure transducer and switch mechanism, either singularly or in combination. For example, U.S. Pat. No. 3,321,594 to Reise, discloses a fluid pressure actuated switch with a diaphragm sensor operatively associated with electrical contacts for controlling an electric fuel pump motor. U.S. Pat. No. 4,255,630 to Hire, also discloses an electrical switch which is responsive to fluid pressure to control a fuel pump motor. U.S. Pat. No. 4,524,255 to Haag, discloses a switch with a movable diaphragm responsive to fluid pressure to open and close contacts of an electric circuit. U.S. Pat. No. 4,581,941 to Obermann, discloses a fluid pressure transducer including a switch therein, adapted to control a fuel pump motor and utilizes a diaphragm and contacts. U.S. Pat. No. 4,805,460 to Betterton, et al., discloses an oil pressure transducer with a piston assembly movable in response to pressure changes and extending to engage a switch.
Several other patents have been found which disclose pressure transducers without the switching device. These include U.S. Pat. Nos. 3,504,324; 4,449,112; and 4,452,202. All of the patents discussed or identified previously, broadly disclose a pressure transducer with or without a switching mechanism but do not specifically disclose the desirable features in the fluid pressure transducer with a switching device, as described hereinafter.
The subject pressure transducer and switch assembly incorporates desirable design features to better monitor and indicate fluid pressure. Specifically, the housing of the transducer forms an enclosure for a piston like member movable along with a diaphragm's mid-portion in response to pressure changes. The piston also carries an electrical contact bearing assembly which engages a resistor board supported by a separate terminal support member. The terminal support member is adjustably inserted into the transducer housing to an extent which determines the pressure indicating calibration and thus, the electrical indicating output.
Therefore, an object of the invention described and claimed in this application is to provide a simple, compact, inexpensive yet reliable fluid pressure responsive transducer having operative parts and assemblies which are conveniently assembled together and therefore, easily serviced and that are associated together in a manner which readily permits calibration of the transducer.
A further object of the present invention is to provide a method for securely fastening the terminals once they have been correctly calibrated. This method is designed to hold positive calibration for the life of the unit as well as make the electrical connections necessary for a properly functioning fuel pump switch.
A further object of the present invention is to provide a solder joint between the insert molded housing ground strap and the ground contact in the terminal support member. Previous transducers have used only a friction interface between the contacting surfaces allowing for possible corrosion which could break electrical contact.
A still further object of the present invention is to provide silver cadmium graphite laminated electrical contacting surfaces so as to enhance the useful life of the transducer.
A still further object of the present invention is to improve the piston contacts with the resistor card so that the piston contacts do not scratch the resistor card tracks. Other objects and advantages will become more apparent when viewed in light of the accompanying drawings and following detailed description.